Nighthowler

Bestow {2}{B}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Nighthowler and enchanted creature each get +X/+X, where X is the number of creature cards in all graveyards.

Meren of Clan Nel Toth

Whenever another creature you control dies, you get an experience counter.
At the beginning of your end step, choose target creature card in your graveyard. If that card's mana value is less than or equal to the number of experience counters you have, return it to the battlefield. Otherwise, put it into your hand.

Cankerbloom

{1}, Sacrifice Cankerbloom: Choose one —
• Destroy target artifact.
• Destroy target enchantment.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Necrotic Wound

Undergrowth — Target creature gets -X/-X until end of turn, where X is the number of creature cards in your graveyard. If that creature would die this turn, exile it instead.

Sibsig Host

When Sibsig Host enters, each player mills three cards.

Massacre Wurm

When Massacre Wurm enters, creatures your opponents control get -2/-2 until end of turn.
Whenever a creature an opponent controls dies, that player loses 2 life.

Blood Artist

Whenever Blood Artist or another creature dies, target player loses 1 life and you gain 1 life.

Plaguecrafter

When Plaguecrafter enters, each player sacrifices a creature or planeswalker. Each player who can't discards a card.

Rakshasa Debaser

Whenever Rakshasa Debaser attacks, put target creature card from defending player's graveyard onto the battlefield under your control.
Encore {6}{B}{B} ({6}{B}{B}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Disciple of Bolas

When Disciple of Bolas enters, sacrifice another creature. You gain X life and draw X cards, where X is that creature's power.

Kaervek, the Spiteful

Gavony Unhallowed

Whenever another creature you control dies, put a +1/+1 counter on Gavony Unhallowed.

Magus of the Order

{G}, {T}, Sacrifice Magus of the Order and another green creature: Search your library for a green creature card, put it onto the battlefield, then shuffle.

Doom Blade

Izoni, Thousand-Eyed

Undergrowth — When Izoni, Thousand-Eyed enters, create a 1/1 black and green Insect creature token for each creature card in your graveyard.
{B}{G}, Sacrifice another creature: You gain 1 life and draw a card.

Farhaven Elf

When Farhaven Elf enters, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Reclamation Sage

When Reclamation Sage enters, you may destroy target artifact or enchantment.

Ravenous Chupacabra

When Ravenous Chupacabra enters, destroy target creature an opponent controls.

Acolyte of Affliction

When Acolyte of Affliction enters, mill two cards, then you may return a permanent card from your graveyard to your hand.

Defile

Target creature gets -1/-1 until end of turn for each Swamp you control.

Sedgemoor Witch

Menace
Ward—Pay 3 life. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 3 life.)
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a 1/1 black and green Pest creature token with "When this creature dies, you gain 1 life."

Grim Haruspex

Morph {B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
Whenever another nontoken creature you control dies, draw a card.

Crypt Lurker

When Crypt Lurker enters, you may sacrifice a creature or discard a creature card. If you do, draw a card.

Radiant Epicure

Converge — When Radiant Epicure enters, each opponent loses X life and you gain X life, where X is the number of colors of mana spent to cast this spell.

Supernatural Stamina

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Dreadmalkin

Menace (This creature can't be blocked except by two or more creatures.)
{2}{B}, Sacrifice another creature or planeswalker: Put two +1/+1 counters on Dreadmalkin.

Syr Konrad, the Grim

Whenever another creature dies, or a creature card is put into a graveyard from anywhere other than the battlefield, or a creature card leaves your graveyard, Syr Konrad, the Grim deals 1 damage to each opponent.
{1}{B}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Arboreal Grazer

Reach
When Arboreal Grazer enters, you may put a land card from your hand onto the battlefield tapped.

Gravedigger

When Gravedigger enters, you may return target creature card from your graveyard to your hand.

Village Rites

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Massacre Girl

Menace
When Massacre Girl enters, each other creature gets -1/-1 until end of turn. Whenever a creature dies this turn, each creature other than Massacre Girl gets -1/-1 until end of turn.

Archetype of Finality

Creatures you control have deathtouch.
Creatures your opponents control lose deathtouch and can't have or gain deathtouch.

Tormod, the Desecrator

Whenever one or more cards leave your graveyard, create a tapped 2/2 black Zombie creature token.
Partner (You can have two commanders if both have partner.)